In searching for increasingly softer and more absorbent disposable towel products, various technologies have been proposed as improvements over the prior art towel products. Traditionally, towel products have been either formed in two plies which are subsequently combined (with or without embossing) or as a single ply with a very high basis weight. Embossing of two-ply products substantially increases the resultant bulk and therefore the consumer perception of softness, and had been the preferred high basis weight product for many years.
Two-ply products have been manufactured either with a laminating adhesive to hold the plies together, or the plies have been jointly embossed so that the embossments effect the lamination. While the embossed products have traditionally exhibited increased consumer perception of softness over a comparable one-ply product, the ply-degradation due to embossing substantially degraded the sheet strength. Two-ply glue-laminated products are usually more absorbent (due to the large void areas between the plies) and stronger than one-ply products, but they have still not exhibited what are believed to be maximum product qualities, especially softness.
An alternative to two-ply towel products are the new generation one-ply products which have competed successfully in the marketplace for some time. While one-ply products may be substantially less absorbent then two-ply products, and without embossing or creping may be quite stiff, they have been considered an economic alternative to two-ply products because they require substantially less converting equipment. In an effort to increase the strength and softness of one-ply products, product improvements are noted in a series of patents issued to the Scott Paper Company, including U.S. Pat. Nos. 3,903,342, Roberts, Jr., 4,208,459, Becker et al and 4,158,594, Becker et al. In these patents, it is proposed to apply a bonding material to a web in a fine pattern, the bonding material serving to bond fibers within the web to add strength thereto, as well as acting as a creping adhesive producing a patterned, differential crepe. The single ply is characterized by high strength (due to the addition of bonding materials in an amount equal to at least 1.4% non-volatile constituents based upon the dry weight of the web), high bulk due to the creping process and softness resulting from the patterned crepe disrupting many of the harsh papermaking bonds.
The Scott patents dealing with single ply products recognized a heretofore unsolved problem with two-ply towel weight products: the finished product should be creped to add softness and bulk. If the plies of a two-ply product had been laminated with embossing, a pressure application to a creping cylinder would de-emboss the web and negate the benefits of the embossment. If the two-ply product had been gluelaminated, attempting to crepe the product would merely crepe one side, since the crepe would not "strike through" to the noncreped ply. Therefore, two-ply products have not heretofore been creped after lamination has been effected. While the one-ply products produced by the processes described in the patents noted above function quite well as towel products, many existing papermaking machines are not adapted to make a single ply towel product (such as 30 to 50 pounds per 2880 square feet), and are therefore limited to making two-ply products. Such machines may be limited to forming sheets having lower basis weights due to limitations in their forming sections. For instance, many "twin-wire" machines inject the fiber stock slurry between two rapidly converging papermaking wires, and basis weight nonuniformities are exacerbated as the basis weight increases. Additionally, some machines may not be operated efficiently at the lower rates of speed necessitated by the high basis weight, such slower speeds being required due to the drying limitations imposed when drying high basis weight webs.
Therefore, a process which would enable a papermaker to produce a two-ply towel product having the increased softness and bulk of new generation single ply towel products would find immediate application to existing papermaking machines.